Support JSDuck v5.x

Add support to JSDuck v5.x with a new "CustomTags.rb" following the new
format (and with a new name for one of the existing flags). Also works
for JSDuck v4.x as before. The call in maintenance/mwjsduck-gen is now
sync'ed with the call made by Jenkins in the CI environment.

Change-Id: Ie6649a3e39457bde7a0d8bd00da8ea53e76e3085